Aluminum Alloy Combining High Strength, Elongation and Extrudability

ABSTRACT

An aluminum alloy includes, in weight percent, 0.70-0.85 Si, 0.14-0.25 Fe, 0.25-0.35 Cu, 0.05 max Mn, 0.75-0.90 Mg, 0.12-0.18 Cr, 0.05 max Zn, and 0.04 max Ti, the balance being aluminum and unavoidable impurities. The alloy may be suitable for extruding, and may be formed into an extruded alloy product.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and is a non-provisionalfiling of U.S. Provisional Application No. 61/653,531, filed May 31,2012, which application is incorporated by reference herein and madepart hereof.

FIELD OF THE INVENTION

The present invention relates generally to an aluminum alloy having highstrength, elongation and extrudability, and in some specific aspects, toan aluminum alloy for use in extrusion and other applications, as wellas methods for processing such alloys.

BACKGROUND

AA6061 is a widely accepted alloy for structural extrusions. There isextensive literature on AA6061 aluminum alloys, including U.S. Pat. Nos.6,364,969 and 6,565,679. It is typically supplied to meet minimumproperties associated with the AA6061 T6 temper:

-   -   240 MPa YS-260 MPa UTS and 8% elongation for section thickness        <=6.30 mm    -   240 MPa YS-260 MPa UTS-10% elongation for section        thickness >6.30 mm

The alloy composition can be improved using relatively low levels of Mgand Si in order to optimise extrusion speed while still meeting thesemechanical property targets. An example of this is U.S. Pat. No.6,565,679. For thick section applications (i.e. >6.30 mm or 0.25 in.)such as anti-lock brake actuator units or heavily machined engineeringparts, a higher yield strength is beneficial to improve machinabilityand also to allow some weight reduction. Uniformity of grain structureis also important to provide uniform machinability, and also becausesuch parts are often anodized, and a mixed recrystallized andnon-recrystallized or “fibrous” grain structure can lead to anundesirable visual appearance. For this reason, a predominantly fibrousgrain structure with a thin surface recrystallized layer is preferredfor such applications. Often the approach to increasing strength in 6XXXalloys is to increase additions of both magnesium and silicon to achievethe required strength levels, but this can be detrimental due to theincreased flow stress and reduced melting point of the alloy.

The present invention is provided to address at least some of theseproblems and other problems, and to provide advantages and aspects notprovided by prior alloys, processing methods, and articles. A fulldiscussion of the features and advantages of the present invention isdeferred to the following detailed description.

SUMMARY OF THE INVENTION

The following presents a general summary of aspects of the invention inorder to provide a basic understanding of the invention. This summary isnot an extensive overview of the invention. It is not intended toidentify key or critical elements of the invention or to delineate thescope of the invention. The following summary merely presents someconcepts of the invention in a general form as a prelude to the moredetailed description provided below.

Aspects of the invention relate to an extrudable aluminum alloycomposition comprising, in weight percent:

Si 0.70-0.85; Fe 0.14-0.25; Cu 0.25-0.35; Mn 0.05 max; Mg 0.75-0.90; Cr0.12-0.18; Zn 0.05 max; and Ti 0.04 max;the balance being aluminum and unavoidable impurities.

According to one aspect, the unavoidable impurities may each be presentat a maximum weight percent of 0.05, and the maximum total weightpercent of the unavoidable impurities is 0.15. According to anotheraspect, the Mn content may be 0.03 max weight percent.

According to a further aspect, the composition may be provided in theform of a billet, ingot, or similar article.

According to yet another aspect, the alloy may be extruded, and theextruded alloy is processed so as to give a substantially nonrecrystallized structure containing deformed grains from the originalbillet. In one embodiment, less than about 20% of the cross section ofthe extruded alloy has undergone recrystallization. In one embodiment,less than about 10% of the cross section has undergonerecrystallization. Such recrystallization percentages may be over atleast a portion of the length of the extruded alloy, over a majority ofthe length of the extruded alloy, or over the entire length of theextruded alloy product.

According to a still further aspect, the alloy has a tensile yieldstrength of at least about 310 MPa and/or a tensile elongation of atleast about 12%.

Additional aspects of the invention relate to a method for processing analloy as described above. Such processing includes extruding thecomposition, press quenching and artificially aging the alloy. The term“press quenching” refers to quenching immediately after the metal exitsthe extrusion die. Prior to extruding, the alloy may also behomogenized. The extruded alloy is then quenched at a rate >10° C./sec,such as by using water mist, spray or quench bath. The quenching may beperformed at a rate >50° C./sec in another embodiment. The alloy may beprocessed to achieve artificial aging, which may be carried out forabout 2-24 hours at an aging temperature of, for example, 160-200° C.The method according to such aspects may produce an extruded aluminumalloy that may have properties as described above.

According to one aspect, the extrusion may be performed at an extrusionratio of less than about 40/1 and/or with an extrusion strain of lessthan about 3.7. According to another aspect, the extruded product mayhave a minimum thickness of at least 6.30 mm or 0.25 in.

Further aspects of the invention relate to an aluminum extrusion orextruded aluminum alloy product formed of an alloy as described above.The extrusion may also be processed as in the method as described aboveand may have properties as described above.

According to one aspect, the extruded products may have a substantiallynon-recrystallized microstructure. For example, in one embodiment, lessthan about 20% of the extrusion cross section has undergonerecrystallization. In another embodiment, less than about 10% of theextrusion cross section has undergone recrystallization. According to afurther aspect, the extrusion may have a tensile yield strength of atleast about 310 MPa in combination with a tensile elongation of at leastabout 12%

The alloy may be used in a wide range of extruded applications and otherproduct forms such as sheet plate or forgings.

Other features and advantages of the invention will be apparent from thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

To allow for a more full understanding of the present invention, it willnow be described by way of example, with reference to the accompanyingdrawings in which:

FIGS. 1 a and 1 b are micrographs illustrating the grain structure ofone embodiment of an extruded alloy according to aspects describedherein; and

FIGS. 2 a and 2 b are micrographs illustrating the grain structure ofone embodiment of an extruded alloy according to aspects describedherein.

DETAILED DESCRIPTION

In general, the alloy composition of the present invention uses acombination of a low magnesium content and a high silicon content,whereas the conventional approach to increasing strength in AA6061 is toincrease both Mg and Si. The resultant alloy may have a solutiontemperature lower than the high Mg-high Si alloys typically used forsimilar applications, allowing for more efficient use of the alloyadditions. The resultant alloy may also have high mechanical strengthand improved extrudability over alternate compositions capable ofsimilar strength levels. The alloy also utilizes Cr addition, and thehigh silicon content and low homogenisation temperature combine topromote a fine Cr dispersoid distribution in the ingot, which increasesZener pinning and suppresses recrystallization and promotes a recoveredfibrous grain structure. The latter may, in turn, provide superiorductility for an equivalent yield strength. Additionally, the alloy mayachieve these strength and ductility increases with excellent efficiencyof utilisation of the alloy additions for strengthening and little, ifany, detriment to extrudability.

The alloy may include silicon in an amount of 0.70-0.85 wt. % or about0.70-0.85 wt. % in one embodiment. As stated above, this level ofsilicon is increased with respect to the silicon levels typically usedin commercial AA6061 alloys. Additionally, this silicon content mayassist in increasing strength, lowering solution temperature, andpromoting a fine Cr dispersoid distribution in the ingot.

The alloy may include iron in an amount of 0.14-0.25 wt. % or about0.14-0.25 wt. % in one embodiment.

The alloy may include copper in an amount of 0.25-0.35 wt. % or about0.25-0.35 wt. % in one embodiment.

The alloy may include manganese in an amount of 0.05 max wt. % Mn orabout 0.05 max wt. % Mn in one embodiment. In another embodiment, thealloy may include manganese in an amount of 0.03 max wt. % or about 0.03max wt. %.

The alloy may include magnesium in an amount of 0.75-0.90 wt. % or about0.75-0.90 wt. % in one embodiment. As stated above, this amount ofmagnesium is similar to the amount of magnesium in AA6061.

The alloy may include chromium in an amount of 0.12-0.18 wt. % or about0.12-0.18 wt. % in one embodiment. As stated above, this level ofchromium is increased with respect to the chromium levels in AA6061. Afine Cr dispersoid distribution in the alloy can increase Zener pinningand suppress recrystallization, as well as promote a recovered fibrousgrain structure.

The alloy may include zinc in an amount of 0.05 max wt. % or about 0.05max wt. % in one embodiment.

The alloy may include titanium in an amount of 0.04 max wt. % or about0.04 max wt. % in one embodiment.

The balance of the alloy includes aluminum and unavoidable impurities.The unavoidable impurities may each be present at a maximum weightpercent of 0.05 or about 0.05, and the maximum total weight percent ofthe unavoidable impurities may be 0.15 or about 0.15, in one embodiment.Additionally, the alloy may include further alloying additions inanother embodiment.

The alloy may be used in forming a variety of different articles, andmay be initially produced as a billet. The term “billet” as used hereinmay refer to traditional billets, as well as ingots and otherintermediate products that may be produced via a variety of techniques,including casting techniques such as continuous or semi-continuouscasting and others. Further processing may be used to produce articlesof manufacture using the alloy, such as extruded articles, which may beproduced by extruding the billet to form the extruded article. It isunderstood that an extruded article may have a constant cross section inone embodiment, and may be further processed to change the shape or formof the article, such as by cutting, machining, connecting othercomponents, or other techniques.

The alloy may have a substantially non-recrystallized structurecontaining deformed grains from the original billet. As described above,the formation of fine Cr dispersoids can assist in achieving thismicrostructure by suppressing recrystallization of the grain structureduring the extrusion (or other hot deformation). In one embodiment, lessthan about 20% of the cross section of the entire extrusion hasundergone recrystallization. In another embodiment, less than about 10%of the cross section of the entire extrusion has undergonerecrystallization. It is understood that the “entire” extrusion or the“entire length” of the extrusion, as used herein, refers to the entiresalable length of the extrusion. In a further embodiment, the aboveamounts of recrystallization may occur over a majority (>50%) of thelength, or over at least a portion of the length of the extrusion. Inyet another embodiment, the above amounts of recrystallization may occuras an average across the entire salable length of the extrusion.

In one embodiment, the alloy or an article produced from the alloy, hasa tensile yield strength of at least about 310 MPa and a tensileelongation of at least about 12%.

The alloy may be processed using one or more of a variety of techniques,such as to form an article and/or achieve desired properties. Asdescribed above, such processing may include extruding the alloy orforming the alloy into an article using a different technique. The alloymay be used for thick gauge extrusions in one embodiment, which haveminimum thicknesses greater than 6.30 mm or 0.25 in., although the alloymay be used in other applications as well. Additionally, an extrusionratio of about 40/1 or less and/or an extrusion strain of less thanabout 3.7 may be used in one embodiment. In one embodiment, the alloyprocessing may include press quenching and/or artificial agingtechniques. The term “press quenching” refers to quenching immediatelyafter the metal exits the extrusion die. Prior to extruding, the alloymay also be homogenized in one embodiment, for example, by heating toabout 550-575° C. for about 2-8 hours or another effectivehomogenization cycle. In one embodiment, the extruded alloy may bequenched (e.g., by press quenching) after extrusion, such as by usingwater mist, spray, and/or quench bath. The cooling rate achieved by suchquenching may be at least 10° C./sec in one embodiment, or may be atleast 50° C./sec on another embodiment. It is noted that the quenchrates reported herein were measured for cooling between 510° C. (i.e.,close to the typical exit temperature) and 200° C. An in situ solutiontreatment may also be accomplished in connection with the quenching.Additionally, in one embodiment, the alloy may be processed to achieveartificial aging, such as by heating for 2-24 hours at an agingtemperature of, for example, 160-200 ° C. Other processing techniquesmay be used in further embodiments.

EXAMPLE 1

The following example illustrates beneficial properties that can beobtained with embodiments of the invention. Four alloy compositions,control (standard high speed AA6061) and alloys A, B, and C were DC castas 101 mm diameter billets, homogenised and cooled at 350° C./h. Aseries of three extrusion tests were conducted using a 780-tonneextrusion press. In each case, the extrusion was water quenched and agedfor 8 h/170° C. Tensile properties were measured on each extrusion andgrain structures were assessed metallographically for the % of the crosssection that was recrystallized. The alloy compositions and test resultsare summarised in Table 1.

The control alloy is typical of a dilute AA6061 alloy used for generalapplications, with a magnesium content close to the AA6061 specificationminimum and silicon content close to the balanced level associated withMg₂Si. The Cr content is <0.10 wt %, which is intended to give adequatetoughness for structural applications without compromising quenchsensitivity and extrudability. The experimental alloys A, B, and C allhad increased Cr additions relative to AA6061, which, as describedabove, can help to promote a non-recrystallized grain structure. Alloy Ahas the Cr level is raised from 0.08 to 0.15 wt % relative to the basealloy AA6061. Alloy B is a typical AA6061 composition used commerciallyin order to try and achieve higher mechanical properties and hasincreased Mg and Si levels for this purpose. Alloy C has similar Mgcontent as the control alloy AA6061 but the silicon content issignificantly higher and the Cr content is higher as well.

TABLE 1 Extrusion Test Results R = 70/1, TB 480 C. R = 70/1, TB 520 C. R= 22/1, TB 500 C. Alloy Mg Si Cu Mn Fe Cr ΔP % YS % El % RX ΔV % YS % El% RX ΔP % YS % El % RX Control 0.80 0.56 0.20 0.01 0.17 0.08 . . . 26411.4 100 100 274 15.4 100 . . . 255 19.8 80 A 0.81 0.55 0.29 0.02 0.170.15 8.8 268 10.4 90 80 289 12.1 95 8.2 284 18.5 27 B 0.98 0.69 0.29<.01 0.17 0.15 9.6 276 10.3 90 50 308 11.3 95 7.5 303 16.5 22 C 0.820.78 0.30 0.01 0.17 0.15 5.2 302 10.9 80 60 339 10 80 4.4 327 16.2 20

Three trials were conducted, using different processing parameters. Asummary of the individual trial conditions follows:

Billet temperature 480° C., ram speed 5-10 mm/s, extrusion ratio 70/1,profile 3×42 mm. The cooling rate during quenching is estimated at 300°C./sec between 510° C. and 200° C. Breakthrough pressure and tensileproperties were measured. The breakthrough pressure values at 8 mm/s ramspeed were compared, and the % increase in breakthrough pressurecompared to the control alloy is presented in column ΔP% in Table 1.

Billet Temperature 520° C., ram speed 5-9 mm/s, extrusion ratio 70/1,profile 3×42 mm. The cooling rate during quenching is estimated at 300°C./sec between 510° C. and 200° C. The maximum ram speed attainable foreach alloy without encountering hot tearing was assessed and therelative extrusion speed vs. the control is expressed as a percentage incolumn ΔV%.

Billet temperature 500° C., ram speed 8 mm/s, extrusion ratio 22/1,profile 50×8 mm. The cooling rate during quenching is estimated at 158°C./sec between 510° C. and 200° C. The breakthrough pressure wasrecorded and the % increase in breakthrough pressure vs. the controlalloy is expressed as ΔP% in Table 1.

[41] The yield strength (YS), elongation (% El) and amount ofrecrystallization (% RX) were measured for all alloys tested in allthree trials. These results are also reported in Table 1.

In test 1, alloy C was the closest of the four alloys to meeting theproperty targets of 310 MPa YS and 12% elongation but did not quite meetthese targets, although the property levels achieved were superior tothe standard AA6061 control and alloys A and B. Surprisingly, thepressure increase for alloy C compared to the control alloy was lowerthan alloys A and B.

In test 2, all four alloys exhibited a strength increase caused at leastpartially by the increased solutionizing effect due to the higherpreheat temperature. Alloy B was close to the property targets but alloyC gave the highest yield strength, well in excess of 310 MPa, and gave ahigher tearing speed than alloy B.

In test 3, alloy B was again close to the property targets, and alloy Cagain had the highest yield strength and exceeded the target strengthand elongation.

In both trials 1 and 2, the extrusions were predominantlyrecrystallized. In trial 3, the lower extrusion ratio produced asubstantially non-recrystallized or fibrous grain structure with ashallow recrystallized layer at the surface (expressed as % RX in Table1—e.g., 100% indicates the full cross section was recrystallized, 20%indicates 20% of the cross section was recrystallized and 80% was nonrecrystallized. This resulted in a significant improvement in elongationfor all four alloys and all four met the 12% elongation target. At thesame time, the billet temperature was intermediate between tests 1 and2, which in turn gave intermediate solutionizing and yield strengthvalues. Under these conditions, alloy C was the only composition to meetthe yield strength and elongation targets. Again, the increase inextrusion breakthrough pressure for alloy C was lower than for alloys Aand B, which was unexpected.

Overall, alloy C gave the best combination of yield strength andductility in all conditions and met the target property values of 310MPa YS-12% El when the extrusion conditions were controlled to give asubstantially fibrous grain structure. At the same time, surprisingly,alloy C required lower breakthrough pressure than alloys A and B, whichcan permit the alloy to be extruded faster at lower cost. These benefitswere obtained with Alloy C for both thick gauge (more than 6.30 mm or0.25 in. minimum thickness) and thin gauge (6.30 mm or 0.25 in. or lessminimum thickness) alloys. Alloy C also exhibited superior hot tearingspeed to alloy B, which represents a typical high strength AA6061 usedin North America today.

EXAMPLE 2

Alloy composition D (0.84 wt. % Mg, 0.77 wt. % Si, 0.29 wt. % Cu, 0.18wt. % Fe, 0.14 wt. % Cr) was DC cast and homogenized as described abovewith respect to Example 1. The billets were extruded into a 3×42 mmprofile at a billet temperature of 500° C. using a ram speed of 5 mm/s.The quench rate at the press exit was varied on successive billets byapplying a slow air quench, a fast air quench, and a standing wave waterquench to give quench rates of 2° C./sec, 8° C./sec and 300° C./sec. Thematerial was aged for 8 hrs/170° C. Table 2 shows tensile properties and% recrystallization values of these samples.

TABLE 2 Quench Test Results (YS and UTS in MPa) Quench Quench Rate °C./sec YS UTS % El % RX slow air 2 252 300 10 30 fast air 8 287 327 1235 water 300 306 337 13 34

As seen in Table 2, the cross section was at least 30% recrystallized inall samples due to the narrow section thickness, and the 310 MPa targetyield strength was not achieved. However, it is clear from the data inTable 2 that fast quenching as achieved by water quenching givessuperior strength and ductility compared to air quenching. Thus, aminimum quench rate of at least 10° C./sec is desirable. While this testwas conducted on a thin gauge alloy, the result would apply to thickgauge alloys (>6.30 mm) as well.

EXAMPLE 3

Alloy composition D (0.84 wt. % Mg, 0.77 wt. % Si, 0.29 wt. % Cu, 0.18wt. % Fe, 0.14 wt. % Cr) was cast and homogenized as described inExample 2 and extruded into a 50×8 mm profile (extrusion ratio of 22/1)using billet temperatures ranging from 475-520° C. and ram speeds from4-10 mm/sec in order to assess the effect of process conditions onmechanical properties. The extrusion was water quenched at the press andsubsequently aged for 8 hrs at 170° C. The cooling rate during quenchingis estimated at 158° C./sec between 510° C. and 200° C. Tensile testingwas conducted using the full section thickness of 8 mm and the grainstructure was assessed at front and back positions along the extrudedlength. The results of this testing are summarized in Table 3 below.

TABLE 3 Extrusion Test Results ram Billet speed exit MPa % RX % RX Temp° C. mm/s temp ° C. YS UTS % El front back 520 4 515 345.7 372.6 15.39.6 9.6 520 6 516 345.3 375.4 14.3 7.7 13.4 500 6 515 344.7 371 15.1 7.714.4 500 8 528 346.5 375.5 16 7.7 13.4 475 8 516 340.6 369 15.8 9.6 13.4475 10 519 342.2 373.6 15.5 9.6 15.3

All the ram speed/billet temperature combinations resulted in an exittemperature >510° C. which is normally considered the target for mediumstrength 6XXX alloys. Typical longitudinal grain structures exhibited bythe tested alloy are shown in FIGS. 1 a and 1 b, which illustrate themicrostructure of a sample extruded at 520° C. with a ram speed of 6mm/sec at the front (FIG. 1 a) and back (FIG. 1 b) of the extrudedsample. As seen in FIGS. 1 a and 1 b, the section core was observed tobe fibrous (non-recrystallized), and there was a thin surfacerecrystallized layer. The depth of this layer is expressed as a % of thesection thickness in Table 3 (%RX). The yield strength and elongationvalues achieved over a wide range of press conditions were well inexcess of the 310 MPa and 12% targets. The depth of recrystallizationincreased from front to back of the extruded length, which is normal fordirect extrusion. The maximum recrystallization recorded was 15.3% atthe back of the extrusion produced at the highest ram speed.

EXAMPLE 4

Alloy D (0.84 wt. % Mg, 0.77 wt. % Si, 0.29 wt. % Cu, 0.18 wt. % Fe,0.14 wt. % Cr) was cast and homogenized as described in Example 3 andthen extruded into a 66×18 mm profile with an extrusion ratio of 7/1.Billet temperatures ranged from 505 to 523° C. and the ram speed wasvaried from 10-30 mm/s which resulted in exit temperatures in excess of510° C. The extrusion was water quenched at the press and subsequentlyaged for 8 hrs at 170° C. The cooling rate during quenching is estimatedat 128° C./sec between 510° C. and 200° C. The test results aresummarized in Table 4.

TABLE 4 Extrusion Test Results ram Billet speed exit % RX % RX Temp ° C.mm/s temp ° C. YS UTS % El front back 521 10 — 369.3 401 16.9 0.9 2.1523 20 537 366.2 396.5 13.4 2.6 3.4 505 30 535 368.9 394.8 15.7 2.1 4.3521 25 542 368.5 396.8 12.5 1.7 4.3

The section was machined to 12 mm thickness around the centerline fortensile testing. On this profile, a yield strength in excess of 360 MPawas achieved with elongation values >12%. Typical longitudinal grainstructures exhibited by the tested alloy are shown in FIGS. 2 a and 2 b,which illustrate the microstructure of a sample extruded at 521° C. witha ram speed of 10 mm/sec at the front (FIG. 2 a) and back (FIG. 2 b) ofthe extruded sample. Again the structure was predominantly fibrous withonly a thin recrystallized surface layer.

The results from Examples 2-4 indicate that with a press water quenchcombined with thick section extrusions, e.g., 8-18 mm, Alloy D canachieve an excellent combination of strength and ductility. The waterquench prevents waste of the Mg, Si and Cu added to the alloy byinhibiting precipitation of coarse non-hardening solute phases duringquenching. Compared to the thinner 3 mm profile, the lower strain duringextrusion associated with the 8 mm and 18 mm profiles maintained the %recrystallization <20% and allowed a good yield strength and ductilitybalance to be achieved. Accordingly, the various embodiments of thealloy described above can produce excellent yield strength and ductilitybalance when used for thick gauge extrusions, such as having anextrusion thickness of 6.30 mm or 0.25 in.

Further, as described above, the lower strain during extrusionassociated with the thicker gauge profiles assisted in maintaining therecrystallization below 20%. The strain in extrusion is proportional tolog_(e) (extrusion ratio) where the extrusion ratio is the crosssectional area of the press container /cross section of the profile. Theextrusion ratios and corresponding strain values for the three profilestested in Examples 1-4 were as follows:

Billet Size Extrusion Ratio Extrusion Strain 42 × 3 mm 70/1 4.2 50 × 8mm 22/1 3.1 66 × 18 mm   7/1 1.9Thus, the various embodiments of the alloy described above can produceexcellent yield strength and ductility balance when extruded using anextrusion ratio of less than about 40/1 and/or an average extrusionstrain of less than about 3.7. It is understood that while the extrusionratio of less than about 40/1 and the average extrusion strain of lessthan about 3.7 are shown in the above example for producing thick gaugeextrusions, this same extrusion rate and extrusion strain may be used bythose skilled in the art in producing smaller gauge extrusions, andsimilar benefits may be expected.

The embodiments described herein can provide advantages over existingalloys, extrusions, and processes, including advantages over typicalAA6061 alloys. For example, alloys described herein may have a solutiontemperature lower than the high Mg-high Si alloys typically used forsimilar applications, allowing for more efficient use of the alloyadditions. Alloys described herein may also have high mechanicalstrength and improved extrudability over alternate compositions capableof similar strength levels. Further, alloys described herein utilize Cradditions, and the high silicon content and low homogenisationtemperature combine to promote a fine Cr dispersoid distribution in theingot, which increases Zener pinning and suppresses recrystallizationand promotes a recovered fibrous grain structure. This may, in turn,provide superior ductility for an equivalent yield strength. Stillfurther benefits and advantages are recognizable to those skilled in theart.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and methods. Thus, thespirit and scope of the invention should be construed broadly as setforth in the appended claims. All compositions herein are expressed inweight percent, unless otherwise noted. It is understood thatcompositions and other numerical values modified by the term “about”herein may include variations beyond the exact numerical values listed.

What is claimed is:
 1. An aluminum alloy comprising, in weight percent,0.70-0.85 Si, 0.14-0.25 Fe, 0.25-0.35 Cu, 0.05 max Mn, 0.75-0.90 Mg,0.12-0.18 Cr, 0.05 max Zn, and 0.04 max Ti, the balance being aluminumand unavoidable impurities.
 2. The alloy of claim 1, wherein theunavoidable impurities may each be present at a maximum weight percentof 0.05, and the maximum total weight percent of the unavoidableimpurities is 0.15.
 3. The alloy of claim 1, wherein the Mn content is0.03 max weight percent.
 4. The alloy of claim 1, wherein the alloy isextruded, and wherein less than about 20% of a cross section of theextruded alloy has undergone recrystallization over at least a portionof a length of the extruded alloy.
 5. The alloy of claim 4, wherein lessthan about 10% of the cross section has undergone recrystallization overthe at least a portion of the length of the extruded alloy.
 6. The alloyof claim 1, wherein the alloy is extruded, and wherein less than about20% of a cross section of the extruded alloy has undergonerecrystallization over an entire length of the extruded alloy.
 7. Thealloy of claim 6, wherein less than about 10% of the cross section hasundergone recrystallization over the entire length of the extrudedalloy.
 8. The alloy of claim 1, wherein the alloy has a tensile yieldstrength of at least about 310 MPa.
 9. The alloy of claim 1, wherein thealloy has a tensile elongation of at least about 12%.
 10. The alloy ofclaim 1, wherein the alloy has a fine Cr dispersoid distribution. 11.The alloy of claim 1, wherein the alloy is extruded, wherein theextruded alloy has a substantially non-recrystallized microstructure,and wherein the alloy has a tensile yield strength of at least about 310MPa and a tensile elongation of at least about 12%.
 12. An extrudedaluminum alloy product formed of an aluminum alloy comprising, in weightpercent, 0.70-0.85 Si, 0.14-0.25 Fe, 0.25-0.35 Cu, 0.05 max Mn,0.75-0.90 Mg, 0.12-0.18 Cr, 0.05 max Zn, and 0.04 max Ti, the balancebeing aluminum and unavoidable impurities, wherein the unavoidableimpurities may each be present at a maximum weight percent of 0.05, andthe maximum total weight percent of the unavoidable impurities is 0.15,wherein the extruded aluminum alloy product is homogenized prior toextrusion, and wherein the extruded aluminum alloy product has asubstantially non-recrystallized microstructure, and wherein theextruded aluminum alloy product has a tensile yield strength of at leastabout 310 MPa and a tensile elongation of at least about 12%.
 13. Theextruded aluminum alloy product of claim 12, wherein less than about 20%of a cross section of the extruded aluminum alloy product has undergonerecrystallization over at least a portion of a length of the extrudedaluminum alloy product.
 14. The extruded aluminum alloy product of claim13, wherein less than about 10% of the cross section has undergonerecrystallization over the at least a portion of the length of theextruded aluminum alloy product.
 15. The extruded aluminum alloy productof claim 12, wherein less than about 20% of a cross section of theextruded aluminum alloy product has undergone recrystallization over theentire length of the extruded aluminum alloy product.
 16. The extrudedaluminum alloy product of claim 15, wherein less than about 10% of thecross section has undergone recrystallization over the entire length ofthe extruded aluminum alloy product.
 17. The extruded aluminum alloyproduct of claim 12, wherein the extruded aluminum alloy product has aminimum cross-sectional thickness greater than 6.30 mm.
 18. A method offorming an extruded product comprising: extruding an aluminum alloyhaving a composition, in weight percent, 0.70-0.85 Si, 0.14-0.25 Fe,0.25-0.35 Cu, 0.05 max Mn, 0.75-0.90 Mg, 0.12-0.18 Cr, 0.05 max Zn, and0.04 max Ti, the balance being aluminum and unavoidable impurities; andquenching the alloy after extruding at a rate of at least 10° C./sec.19. The method of claim 18, wherein the extrusion is performed at anextrusion ratio of less than about 40/1, and the extruded product has aminimum cross-sectional thickness of at least 6.30 mm, and wherein lessthan about 20% of a cross section of the extruded product has undergonerecrystallization over at least a portion of a length of the extrudedproduct, and wherein the extruded product has a tensile yield strengthof at least about 310 MPa and a tensile elongation of at least about12%.
 20. The method of claim 18, further comprising homogenizing thealloy prior to extruding.
 21. The method of claim 18, wherein thequenching comprises press quenching performed by using water mist, sprayor quench bath.
 22. The method of claim 18, further comprisingartificially aging the alloy after quenching, wherein the artificialaging is carried out for 2-24 hours at an aging temperature of 160-200°C.
 23. The method of claim 18, wherein less than about 20% of a crosssection of the extruded product has undergone recrystallization over atleast a portion of a length of the extruded product.
 24. The method ofclaim 23, wherein less than about 10% of the cross section has undergonerecrystallization over the at least a portion of the length of theextruded product.
 25. The method of claim 18, wherein the extrudedproduct has a tensile yield strength of at least about 310 MPa and atensile elongation of at least about 12%.
 26. The method of claim 18,wherein the alloy is extruded to a minimum thickness of at least 6.30mm.
 27. The method of claim 18, wherein the extrusion is performed at anextrusion ratio of less than about 40/1.
 28. The method of claim 18,wherein the extrusion is performed with an extrusion strain of less thanabout 3.7.
 29. The method of claim 18, wherein the quenching is at arate of at least 50° C./sec.